This study proposes to investigate various endocrine influences on the growth and development of fetal lung with particular reference to the surfactant synthesizing system. The long term goal is the development of means for the prevention of hyaline membrane disease. The study is divided into two interrelated sections. First the influence of certain fetal and maternal hormones on the growth, cytodifferentiation and composition of lung will be investigated during periods of prenatal and postnatal development. The effect of hormonal treatments or deficiencies during the pre- and postnatal periods will be evaluated in terms of lung cell proliferation, type II pneumocyte concentration and surfactant production. The periods in lung development during which certain hormones influence surfactant activity will be studied and correlations made with hormone receptor activity during these periods. Studies will also be made of the role of glycogen (whose synthesis and degradation are known to be under hormonal control) in the synthesis of surfactant during the fetal period. In other studies, the influence of neurohumoral agents on surfactant secretion will be evaluated. In a second group of experiments, the growth, cytodifferentiation, composition, and surfactant producing abilities of lung organ and monolayer cultures will be evaluated. The influence of specific hormonal additives or deficiencies on these processes will be tested in such in vitro systems. The development and localization of the glucocorticoid receptor system will also be studied in the mesenchymal and epithelial components of embryonic lung grown in vitro.